Process for preparing olefins from alkyl halides



H. E. Buc 2,368,446

PROCESS FOR PREPARING OLEFINS FROM ALKYL HALIDES Jan. 3o, 1945.

Filed July 1o, 1940 l'. I' n NWQOOU lll NWS FQUWN III'I Inu . IIIIIII N1 N, h"ill u WS; 0IA

Patented Jan. 30, 1945 2,368,446 raoonss Fon-PREPABING oLEFrNs FaoM Amm. HALmEs Hyym E.

ard Oil of Delaware Buc, Roselle, N. if., assignor to Stand- Development Company, a corporation Application July 10, 1940, Serial No. 344,657

11 Claims. (Cl. 260-677) This invention relates to an improved method for obtaining oleflns from alkyl halides which is of especial value in the separationof tertiary olens fromrmixtures with other olens as in cracked petroleum products.

The tertiary olens, such as isobutylene and trimethylethylene, can be readily separated from mixtures, such as cracked petroleum fractions, containing'saturated and other unsaturated hydrocarbons, such as butene-l, butene-Z, namylene-1 and -2, isoamylene and the like, by treating the mixtures with a hydrogen halide under conditions such that only the tertiary olens react, with the formation of tertiary alkyl halides. For example, a mixture of saturated and unsaturated hydrocarbons of 4 carbon atoms, known as the C4 cut and obtained by fractional distillation of cracked petroleum products, may be treated with anhydrous hydrogen chloride at about 78 C., and the isobutylene contained in the .mixture will thus be converted substantially completely to tertiary butyl chloride, there being no appreciable reaction of hydrogen lchloride with either the butene-l or butene-Z contained in the hydrocarbon mixture. A similar selective reaction may also be secured with concentrated aqueous hydrochloric acid at room temperature, the reaction being much more rapid. The tertiary alkyl halides thus formed may be separated from the unreacted hydrocarbons by any 'suitable method,rsuch as solvent extraction and/or fractional distillation, and theseparated tertiaryalkyl halides may then be treated to recover therefromvthe tertiary oleiins.

Tertiary amyl chloride, for example, may be decomposed to trimethylethylene and hydrogen chloride by passing it at a temperature of 300- 350 C. over bauxite or other suitable contact and the hydrogen halide is reduced substantially to a minimum. The olefin isthus recovered in substantially theoretical yields and the separated hydrogen halide is in condition for immediate return to the zone in which the initial treatment \of further amounts of cracked petroleum iractions or other mixtures of oleiins is performed.

A solvent for the hydrogen halide may also be used in conjunction with the solvent for the olefin, provided that the two solvents are substantially immiscible with each other. In this case, it is desirable to separate the two solvent phases as quickly as possible after the absorption is carried out. For example, oil and water may be used as the respective solvents, and e resulting oil solution of olens may be separa ed from the aqueous hydrogen halide by gravit this separation may be accelerated by means of a centrifuge. The aqueous hydrogen then be returned for further treatment of additional olefinic stocks, and thespent or weak solution of aqueous hydrogen halide resulting from this latter treatment may be used as the solvent for hydrogen halide formed in the dissociation of the tertiary alkyl halides, and may be thereby fortified for further use in the treatment of olerlnic stocks.

flow of materials.

material. However, owing to the ease with which the decomposition products, namely, the tertiary olefin and hydrogen halide, recombine even at room temperature, the separation of these decomposition products 'lias heretofore been in-j` complete and ineicient.

It has now been foundthat the dissociation products, namely, the tertiary olefin and Vhydrogen halide, can be readily separated without loss by bringing the mixture into Contact with a selective solvent for the olen before the temperaturehas been reduced to a point at which recombination is appreciable and/or so quicklyy tial setional elevation of suitable equipment for carrying out a process which illustrates the present invention which is in no way limited to the particular apparatus described, and indicates the Similar index numbers refer to similar parts throughout the gure of the drawing.

Referring to the drawing in greater detail, a'

ymixture of secondary and tertiaryk olens such as a cracked fraction or preferably the C4 or Cs cut thereof is passed by line i into tower 2 which is maintained at a suitable temperature for the desired reaction. A hydrogen halide such that such recombination of olefin and hydrogen halide is largely avoided. In this manner, any

dilution or loss of the hydrogen halide is avoid-- edv/,and the extentof recombination ofthe olen fas a concentrated aqueous solution of hydrogen chloride is supplied by line 3 to the tower 2 and is brought into countercurrent contact therein with the olen mixture. The excess hydrogen halide is then withdrawn as a relatively dilute aqueous solution from the bottom of the tower by line 4 and may be passed by line 5 to suitable equipment for absorption of hydrogen halide and reconcentration as will be described hereinafter.

halide may The tower 2 is maintained under suitable conditions of temperature and pressure for the formation of the desired alkyl halide; for example, it may be controlled for the selective reaction of the tertiary olens to form tertiary alkyl halides, with no appreciable reaction of secondary olens with the hydrogen halide. It may also be provided with any suitable catalysts for promoting the desired reaction, such as alumina, silica gel, antimony trichloride, calcium chloride, and the like. The mixture of alkyl halides and unreacted hydrocarbons is withdrawn by line `B and is passed through heater 1 into a distillation column 8. This mixture may be first washed with water or neutralized with any suitablev base to remove any unreacted hydrogen halide, and to prevent reaction thereof with other olens before the temperature of the mixture is raised. Any unrea-eted hydrocarbons are removed from the top of column 8 by line 9 and the alky1 halides are withdrawn byline I0. They are then passed through a heating coil or other suitably heated reaction chamber I I in which they are heated to a temperature suicient to cause dissociation into olenand hydrogen halide. The dissociation may be promoted by bauxite or other suitable catalysts such as alumina, silica, carbon, activated carbon, platinized-asbestos, or the chlorides of metals such as nickel, cobalt, iron,`cadmium, lead, barium and calcium. The hot dissociation products may then be passed quickly through a cooling coil I2 or through Iby-pass line I3 and line I4 into the lower portion 'of a tower I5. This tower is preferably provided with suitable Icooling means such as the pipes' I6 for indirect heat extraction, by means of a cooling fluid circulated therethrough, from the materials within the `tower I5. The dissociation products from line I4 are brought quickly into contact in tower I5 with a mixture of immiscible liquids, one having a selective solvent action for the oleiins, such as a hydrocarbon oil, and the other having'a selective solventaction for the hydrogen halide, such as water or a weak aqueous solution of hydrogen halide. These solvents may be supplied to the upper portion of the tower I5 by the line lIr and may pass down the tower countercurrent to the rising stream of dissociation products. These products are thus cooled in the cooler I-2 and/or in the tower I5 to a temperature suiiicient to permit substantially lcomplete absorp- -tlon by the selective solventasuch as about C. or a preferably lower temperature. Any undissolved products, such as fixed gaseous decomposition products, leave the top of the tower by line I8. The mixed solutions of the olenand hydrogen halide leave the tower by line I and are quickly passed into a suitable separator, such as the centrifuge 20. The oil'layer is separated therein lfrom the water layer and is withdrawn through line 2l and then passed through suitable distillation equipment such as the tower 22 by which the oleiin is distilled overheadthrough line 23 and is collected in receiver -24 while the solvent, substantially freed of olefin, is withdrawn by line 25'and-is returned -after cooling to tower I5 by line I1. A portion of this solvent may also be passed through line 26 into directl contact with the dissociation products leaving the reaction vessel II and may thus be used-to quench these products rapidly to any desired temperature. The dissociation products may also be iirst partially cooled in cooler I2 before contact with the quenchingV oil by means' of line 21, in order to avoid any undesirable reaction therewith.

The water layer -iswithdrawn from the sepalrator 20 by line 28 and maybe returned directly to the tower 2 by lines 29 and I for further treatment of olenic materials. The relatively dilute aqueous hydrogen halide leaving the tower 2 by line 4 may be passed by lines 5 'and I1 to the tower I5 for absorption of lhydrogen. halide from the alkyl halide dissociation products. Water may be supplied for this purpose by line 30.

The alkyl halide dissociation products may also be brought into contact with only a single s elective solvent for one component thereof, e. g., the 'toweri 5 may Ibe supplied only with oil to dissolve the olefin, and the unabsorbed hydrogen halide may be withdrawn from` th topY of the tower by line IB.

In this case the hydrogen halide in line I8 may be dissolved in water or in the weakened hydrogen halide lfrom line 5 and the reconcentrated hydrogen halide returned to line I for further use.

if it is desired to conduct the hydrohalogenati'on with a dry hydrogen halide, this absorption in water Imay be omitted and the hydrogen halide in` line I8 may be used directly. The reaction with dry hydrogen halide is usually much slower, however, and is preferably conducted under pressure.

The following example illustrates the application of this invention to the separation of trimethyl-ethylenefrom a cracked petroleum fraction containing other olefins.

A cracked petroleum fraction boiling between vabout 25 and 40 C. and known as the "Cs cut is treated with aqueous hydrogen chloride (30 to 36% concentration) at a temperature of 20 to '25 C. and under atmospheric pressure in order to convert selectively the trlmethyl-ethylene contained in this fraction into tertiary amyl chloride. The hydrogen chloride is used in such amount that its lconcentration is reduced to about 25% by this reaction, at which concentration the reaction rate becomes quite slow. Following the completion of this reaction, the aqueous phase is sepa'- rated from the non-aqueous phase, and the latterv is distilled in order to separate the unreacted hy.- drocanbons from the tertiary amyl chloride. The" tertiary amyl chloride is then passed over bauxite or other suitable catalyst, such as clay impregnated with phosphoric acid, at a, temperature of 320 C., and is thereby dissociated to the extent of about 90% into amylene and hydrogen chloride. The dissociation products are cooled quickly to aboutl 10 to 20 C., and are then passed directly into contact with an amount of an oil,

such as a, fuming acid-treated kerosene or straw' oil, suilicient to absorb the amylene. The unabsorbed vapors are then passed through water. Titration of the hydrogen chloride absorbed in the water indicated that of the tertiary amyl chloride was dissociated into amylene and hydrogen chloride.

If the dissociationproducts leaving the dehydrochlorination zone in'theabove-described process are passed through ordinary condensers so. as

to condense the amylene and undecomposed amyl chloride, no oil solvent for the an'lylene beingused, there results only a 40 to 50% yield of amylene (based on the emyl chloride treated) the remainder of the amylene undergoing recombination with the hydrogen chloride.

The process of this invention is useful for the dissociation of organic halides generally into oleiins and hydrogen halide, and is particularly advantageous in instances where the organic halide is formed by reaction cian olefin with hydrogen;

halide 'in the course oi.' the separation o1 the olefin from other materials less reactive with hydrogen halide. In the application of the present invention to the latter process, a particularly advantageous feature is that the hydrogen halide liberated in the dissociation of the alkyl halide is available for recirculation to the initial stage of the process, in which it reacts with the desired oleiln to form an alkyl halide which is separated from the unreacted materials with which the olefin was associated by a method making use of the difference in volatility, solubility, or other characteristics of the tertiary alkyl halide and the associated materials. The process of the invention is especially applicable to the dissociation of tertiary alkylhalides of 4 to 6 or more carbon atoms per molecule and the recovery of the corresponding tertiary olens from the dissociation products, although it is also applicable lto the treatment of olen-hydrogen halide mixturesobtained in the dissociation of organic halides broadly. z

The selective solvent used to absorb the olens is preferably one that is non-reactive Awith hydrogen halides. Examples of such solvents are the organic halides, such as dichloroethane. Hydrocarbon oils are especially preferred, however,

because oi the extremely low solubility of hydrogen chloride in them and their ability to retard Arecombination of the olefin with the hydrogen halide in the dissociation products being treated. The hydrocarbon oil is preferably of a saturated nature and of suitably high boiling point to permit ready separation of the dissolved olefin therefrom. Kerosene or straw oils boiling preferably above about 400 F. are examples'of suitable hydrocarbon oils, although even heavier fractions may be used. Such oils are preferably substantially inert to hydrogen chloride and may be either distillate fractions of suitably saturated crude oils or of crude oils which have been treated with strong or, preferably, fuming sulfuric acid to remove constituents which are reactive with hydrogen chloride.

It is claimed:

l. Improved process for obtaining an oleiin from an organic` halide comprising heating said organic halide in the vapor phase to a dissocia tion temperature, passing the resulting mixture of olefin and'hydrogen halide immediately into contact with a liquid organic solvent having relatively high solvent power for olens and relatively low solvent power for hydrogen halide, at a temperature at which said solvent is unvaporized, to selectively dissolve said olefin, and separating the solution of said oleiln in said solvent from contact with said hydrogen halide.

2. Improved process according to claim. 1 in which said organic halide is a tertiary organic halide.

' selective solvent for -said mono-olefin, which sol- 3. Improvedprocess according to claim 1 in ethylene from tertiary amyl chloride comprising heating tertiary amyl chloride in the vaporphase to a dissociation temperature, passing the resulting mixture of trimethylethylene and hydrogen chloride immediately into contact with a substantially saturated hydrogen oil boiling mainly above 400 F. which is a selective solvent for the trimethylethylene, and separating the resulting solution from contact with the hydrogen chloride.

8. Improved process for obtaining a tertiary oleiin from a tertiary alkyl halide comprising heating said tertiary alkyl halide in the ,vapor phase to a dissociation temperature, passing the resulting mixture of tertiary olen and hydrogen halide quickly into Contact with a mixture of water and a water-,immiscible selective solvent for said olen, under suitable conditions for .the absorption of said olen, and separating the resulting solution of said oleiin from the aqueous solution of said hydrogen halide.

9. Improved process for obtaining a monoolefin from an alkyl monohalide comprising heating said alkyl halide in the vapor phase to a dissociation temperature, immediately cooling the resulting mixture of mono-olen and hydrogen halide quickly to about 10 to 25 C. and bringing it -immediately into contact ,with a liquid organic vent is inert to hydrogen halide and boils 'above the boiling point of the mono-oleiin, and separating the solution of said mono-olefinv in said solvent from contact with said hydrogen halide.

10. Improved process for obtaining trimethylethylene from tertiary amyl chloride comprising heating tertiary amyl chloride in the vapor phase to dissociation temperature, immediately cooling the resulting mixture of trimethylethylene and hydrogen chloride quickly to a temperature below about 25 C. and bringing it immediately into intimate contact with a liquid organic selective -solvent for the trimethylethylene, which solvent is inert to hydrogen halide and boils above the boiling point of the oleiin, and separating the resulting solution of said olefin in said solvent l from contact with the hydrogenl halide.

l1. Improved process for obtaining al tertiary mono-olen from a tertiary alkyl monohalide comprising heating said tertiary alkyl halide in the Vapor phrase to dissociation temperature, cooling the resulting mixture of tertiary olefin and hydrogen halide quickly to a temperature below ,about 25 C. and bringing it immediately into intimate contact with a mixture of water and a water-immiscible selective solvent for said oleiin, which solvent is inert to hydrogen halide and boils above the boiling Ipoint of the olen, and

separating the resulting solution of said olefln in said solvent from the aqueous solution of said hydrogen halide.

HYYM E. BUC. 

